Optical switching devices may be classified as either passive or active optical switches. Typically, a passive optical switch receives incoming light and changes state based upon the received light; some employing photon absorption for activation and others all-optical components and organic dyes. An example of an optical switch acting as a limiter employing photosensitive compositions is disclosed in U.S. Pat. No. 6,652,778 ('778 patent) to Twarowski. The '778 patent discloses a reversible thermochromic optical switch that incorporates a thermochromic material which is transparent to light at ambient temperature, but turns to a colored state when incident laser radiation causes localized heating, thereby reversibly limiting the transmission of laser radiation. A further example of a passive optical switch acting as a limiter is found in U.S. Pat. No. 5,737,102, to Asher, which disclosed the use of charged particles in a surrounding medium wherein inclusions are added to either the particles or the medium that have a highly nonlinear refractive index. Upon high intensity radiation the refractive index changes. In another embodiment, a nonfluorescent, photoabsorptive dye is incorporated into either or both the particles or medium. Upon being impinged with high intensity radiation, the dye absorbs photons. The drawbacks of passive devices include limited dynamic range and the threshold for operation may be intolerably high, effectively preventing the device from performing its intended function.
In contrast to passive optical switching, active optical switches are activated and/or deactivated by a power signal. An example of active optical switching is found in, for example, U.S. Pat. No. 6,128,115 to Shiragaki, entitled “Optical Switch Device.” The '115 patent discloses an optical switching device comprising a plurality of multi-functional wavelength converters in which an input terminal and an output terminal are connected to optical divider and optical coupler wherein a wavelength converter is operative only when a current flows through a semiconductor optical amplifier in the wavelength converter. By turning on/off the current flowing through the semiconductor optical amplifier in the wavelength converter, the wavelength converter functions as a gate switch.
Although optical switches may be employed in telecommunications and fiber optic technologies, active optical switches are not typically employed in the transmission of images in an original, un-encoded state as is readily accomplished with a passive device.
Group III-V semiconductor compounds, such as indium gallium nitride semiconductors, used in connection with light emission devices are well known. For example, in U.S. Pat. No. 6,649,440, to Krames, et al., hereby incorporated by reference as though fully rewritten herein, there is disclosed a light-emitting diode (LED) formed from various Group III-V semiconductor compounds. One embodiment of the LED disclosed in the '440 patent includes a thick multi-layered epitaxial structure comprising an upper and lower AlGaInN region, and an active region therebetween, which may be formed of indium gallium nitride. The '440 patent is directed to increasing the luminous intensity of the emitted light. Heretofore, semiconductor compound devices have not been employed in limiting the intensity of a beam of radiation in connection with the an actively switched optical limiter which absorbs or reduces the intensity of a laser light beam, and which is portable, reliable, and durable